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Spring steel won't skate a file


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Hi all I've recently been making a Bowie fighter for a friend and its gone really smoothly and nice considering it's my most complex build to date... up until now. 

I'm having trouble with hardness, I've normalised three times and then went for a quench after getting up to temp. I get some hardness from the file doesn't quite bite as much but it definitely doesn't skate a file either. I tried the quench again but the same thing occurred. I then used a scrap of the same steel and tried a water quench which got it to the same hardness roughly of the oil quenched blade. I know I'm obviously working with an unknown steel as it's from a Landover leaf spring, the oil I used was veg oil which worked excellently for a file knife I forged up a while ago.

Any help or in site at all would be much appreciated as I really want this knife to get hard after all the work that's gone into it. But I understand the nature of working with the beast of unknown steel.

Many thanks for your time

 

Edited by Byron studley
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Try removing more metal from the edge(just a small amount). It could be an issue of decarb. How are you getting a temperature read? Magnets are not a good guage, nor color, or a thermocouple on salvaged mystery steel. Look for the recalescence shadow in the steel. Pictures of the blade and more info. about your process could actually help us determin where you went wrong. I suspect you are quenching too cold. If it is 5160 it will go nonmagnetic way before it's at critical.

Edited by Zeb Camper
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Hi thanks for the reply. I must admit I've got a relatively low tech setup as I'm quite new to this. I was just testing for non magnetic. It was a bright orange colour when I quenched. If I can get an infrared thermometer what temp would you suggest I get. 

As for the decarb, is that an issue with the edge just being to thick or is it that I've lost carbon during my normalising cycles? Also quenched an offcut that hadn't been subjected to the forging process and normalising and that also didn't get hard so would that point more towards a temp issue that a decarb problem? 

 

Edited by Byron studley
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Decarb. Is a loss of carbon caused by repeated heating in an oxidizing atmosphere (not a neutral flame). You can not go by temperature on junk steel. The most accurate way to know it is ready to quench is to look for something called "recalescence". Here's a post with way more info. Than you need :)

 

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And just to be clear, you heat the blade and pull it out of the forge to check for the shadow. Once it's visible, continue to heat it as evenly as possible. Heat the thick parts first, then move out towards the thinner parts. Keep checking your shadow outside of the forge until thr shadow is just gone, then quench. It's best to do this in low light (Like at dusk with the lights off) 

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Thanks that post was helpful, I will take the steel down in thickness a bit and  try to go for another quench when it gets dark in a few hours and I will watch for that. So the theory is that I watch for recalescence whilst heating and that is the indicator that it's ready for quench? 

If in the event I quench after recalescence and the file still doesn't skate is it likely that the steel has reached its maximum hardness? 

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Make no mistake it's not a theory. It's the proper way to do it. I heat treat all my blades like that. I just didn't know all the science behind it until recently. You don't need to know the science really, just make sure that shadow is barely gone. You probably don't need to thin the blade down right now, but after the quench you might be hard further down and have a softer outside. just be aware of that when file testing. It might read soft for a while, and after filing for a while you'll see that it's Starting to skate. 

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I would try a scrap piece first. It takes some people a while to figure out what to look for. Heat it up really hot, and let it cool. Watch for the recalescence shadow to form. Now you know what to look for. Then, just do the opposite with the scrap metal by heating it until that shadow is gone and quench. It should be hard. Then do the knife the same way. Once you get good at this, there's no need for any fancy equiptment. 

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Also, don't have the forge on full blast. You want it pretty cold actually. on short to medium blades I run mine at the manufacture's minimum pressure of 3psi.

I would pick up some canola, or peanut oil. That veggie oil is rumored to go bad. Possibly causing a viscosity change which will equal a slower quench. Remember to preheat the oil with some hot scrap metal to the point where it's uncomfortable to touch with your finger.

Edited by Zeb Camper
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Thanks so much for all the info, like I said I'm pretty new to this it's only my second knife, I'm good at research and reading up on things, but as you know its about putting it into practice. I've just cleaned the knife up a bit and taken a bit of metal off with the 40 grit belt. Just going to wait for it to get dark here and I'll try again. 

Considering I've now quenched twice would it be wise to do one more normalising cycle before try the quench?

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Second knife!? Looks pretty badass to me! You might want to thin the profile of that tang some so you can put a sexy handle on it. In my opinion the handle needs to be as wide as the ricasso on the other side of the guard. Doesn't look like you have enough room for the outer walls of the handle to be very thick. You might want to re normalize. Remember to go over critical on the first one, then just under critical, then end at a low red heat for the last cycle. Otherwise you'll get alloy banding. Thats a good looking knife! Welcome to the forum!

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one last thing... It wouldn't be a  bad idea to go to forging heat to grow the grains a bit, then normalize. You actually can refine the grains too much, causing you to have poor edge retention. Good luck, please share the results!

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Being Land Rover spring it's probably EN43, which is closer to the US designation of 9260.  Silicon instead of chrome, and it will certainly get hard!  It's tough stuff, too.

Zeb has given you good advise, although over-normalizing doesn't reduce edge retention.  It will make that steel more shallow-hardening, though.  Nice shape, by the way!

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Thanks guys I've gone back and tried another quench now it's dark. I followed the recalescence shadow until it had disappeared. Held it for a little longer then quenched. It is harder than it was! It does skate a file but it tends to bite in on a few spots, could this be a problem with my normalising? 

Anyway it's in the Tempering oven for a cycle I will give it a couple rounds of Tempering and I will see how it fairs tomorrow.

As for the tang needing thinning down I had planned to do that post heat treat, I will be drawing the tang right back temper wise anyway and I wanted to make sure I left a little meat on it. I had a warped tang on my first blade and I figured if I left a bit of room on this one I could grind it out if I did get a warp.

Handle wise I let the future owner pick out the material, he's a close friend who does anti-poaching in south Africa. He selected some wild African olive wood. It look really nice.

Can't thank you guys enough for all the help it's much appreciated! 

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Oh ok thanks, it's been a day for learning today. 

Also any tips on the Tempering for this steel, I did the first cycle of an hour at 170 Celsius which I think is around 340 F. I was then going to leave it 24 hours and do a second cycle the same as the first. 

I've read on a different forum that leaving it 24 hours between cycles is important, is this correct? 

Edited by Byron studley
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Lots of debate on the timing between cycles. IMO allowing it to go cold in still air is all I've needed with the steels I use.

Not sure about the steel you are using but 340f seems awfully low to me. There are others here who know it better than I.

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Yeah, I think I would start at 400°F and temper up for a fourth cycle if you think it's still too hard. I would just let it cool in still air, then pop it back in the oven. Waiting 24 hours wouldn't hurt it any. Not sure If it would help or not. If you have soft spots, I would file on them for a while to see if you eventually hit hard steel. If not, you'll have to try quenching again. Is it by any chance soft just above the ricasso? If so, I think that area just didn't get hot enough. This is good though, you may have been off by only a tiny amount. You likely aren't overheating it any though which is why I say it's a good thing. You just need to adjust your technique a tad, and you'll be getting it just right. 

Edited by Zeb Camper
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You can actually quench in water right out of the oven and stick it back in.  Tempering is not hardening or normalizing, after all.  The 24 hour thing is for complex steels with lots of retained austenite that continues transforming to martensite over a period of time.  The steels this helps are not common stuff, though.  I did a competition cutter out of 9260 a few years back and tempered one cycle at 375 f, one at 350 f, and one at 325 f.  It was able to take a sliver of steel off the cutting table (accidentaly!) with no edge damage.

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Ok so I tempered for a second cycle at 190°C which I believe is 375F roughly, and this is how the colours came out. Now I've heard that you are aiming for the straw golden colour as is on the tip end of the knife, has the belly gone too far?

As for the soft spots the spine had most of them there was a slight bite on the file when I ran the file along the very edge of the knife but the file didn't bite on the flats of the bevels (which I gave a quick sand on the 40grit to clean up post quench) so I'm hoping that on the very edge it's decarb. Does this sound about right? 

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